Investigation of Thermal Stability Effects of Thick Hydrogenated Amorphous Silicon Precursor Layers for Liquid‐Phase Crystallized Silicon

Abstract

The thermal stability of thick (≈4 μm) plasma‐grown hydrogenated amorphous silicon (a‐Si:H) layers on glass upon application of a rather rapid annealing step is investigated. Such films are of interest as precursor layers for laser liquid‐phase crystallized silicon solar cells. However, at least half‐day annealing at T ≈550 °C is considered to be necessary so far to reduce the hydrogen (H) content and thus avoid blistering and peeling during the crystallization process due to H. By varying the deposition conditions of a‐Si:H, layers of rather different thermal stability are fabricated. Changes in the surface morphology of these a‐Si:H layers are investigated using scanning electron microscopy and profilometry measurements. Hydrogen effusion, secondary‐ion mass spectrometry (SIMS) depth profiling, and Raman spectroscopy measurements are also carried out. In summary, amorphous silicon precursor layers are fabricated that can be heated within 30 min to a temperature of 550 °C without peeling and major surface morphological changes. Successful laser liquid‐phase crystallization of such material is demonstrated. The physical nature of a‐Si:H material stability/instability upon application of rapid heating is studied.

Secondary Ion Mass Spectrometry Study of Hydrogenated Amorphous Silicon Layer Disintegration upon Rapid (Laser) Annealing

“…We think that this disintegration effect can be considered to serve as a model for the peeling of a‐Si:H films which may be of importance, for example, for the fabrication of silicon on glass devices like solar cells. [ 11 ] This effect is observed for intrinsic as well as B‐doped a‐Si:H films.…”

“…[22,23] We note that such a disintegration mechanism may not be confined to a-Si:D/a-Si:H layer interfaces and may well occur within entirely amorphous a-Si:H material at planes defined by high strain. [11] These effects need to be considered when a-Si:H films are annealed, in particular, at high heating rates. Our results show, furthermore, that a high H diffusion length alone does not necessarily lead to disintegration, see Figure 5b and 8.…”

“…In recent time, interest has increased in details and mechanisms of a-Si:H film disintegration and peeling. [8,[11][12][13] These latter effects are known to occur mostly during annealing, in particular involving rapid heating. Related to such disintegration effects may be bubble and pinhole formation due to accumulation of H at interfaces.…”

Origin of the Unusual High Optical Nonlinearities Observed in Glassy Chalcogenides

“…Non‐chalcogenide amorphous compounds show either low polarizability as nitrides or oxides, or low stability as in case of a‐Si. [ 38 ] However, excellent performances are reported in amorphous As‐based chalcogenides. [ 39 ] Arsenic is a good chalcogenide glass former since it stabilizes the chalcogenide.…”